The long term objective is to develop the capability to build large arrays of energy dispersive x-ray detectors for installation and use at Synchrotron Radiation (SR) and other x-ray research facilities. Each array element would have energy resolution of 300 eV or better at 6 KeV and a count rate capability exceeding 50,000 cps. Completed arrays, containing upwards or 100 elements, could count at rates over 5x10-6 cps and are targeted to cost less than $l00,000. Coupled to the next generation of high brightness SR x-ray sources, these arrays would lead to a greatly enhanced ability to obtain the direct structural information which has been found to be so useful in unravelling the mechanisms by which proteins and enzymes function at the molecular level. The arrays could be organized either linearly, as diffraction detectors, or 2-dimensionally as fluorescence detectors for XANES and EXAFS. The projected increases in countrate capability and solid angle collection efficiency would make research possible at ultra-low dilutions or as a function of time, temperature, or concentration which would otherwise be unfeasible or impossible with currently available sources and detectors. This proposal's specific goal is to develop a small, 4-10 element front end subassembly, including preamplifier electronics and mounting package, which meets the performance criteria stated above and which can linked together to form larger scale arrays. The subassembly components to be developed and assembled include a Mercuric Iodide multiple detector element, a hybridized multichannel preamplifier, and an assembly package to mount and slightly cool both detector slice and front end FETs. A major testing effort will be implemented to assure overcome expected problems with resolution limiting noise and crosstalk between channels. Finally, a planning effort will examine the electronics, computer, and software requirements necessary to integrate these subassembly modules into finished, fully functioning, easy to operate arrays.